Air filter wash device

ABSTRACT

Apparatus for cleaning filter elements comprising a plurality of nozzles for spraying water mounted asymmetrically with respect to the filter element to provide an asymmetric spray pattern whereby optimum utilization of the available water supply is obtained.

United States Patent lnventor Joseph William Robinson 1632 Midland Ave.,Scarborough, Ontario, Canada Appl. No. 697,393 Filed Jan. 12, 1968Patented Feb. 16, 1971 AIR FILTER WASH DEVICE 6 Claims, 13 Drawing Figs.0.8. CI 239/56 1 134/172; 239/566, 239/597 Int. Cl B05b 1/14 FieldofSearch 134/167,

'181,(lnquired); 239/(lnquired);239/566, 561, 597; 134/172, 198

[56] References Cited UNITED STATES PATENTS 2,467,502 4/1949 Scofield239/561X 3,055,158 9/1962 Smith 134/172X 3,217,987 11/1965 Valtanen eta1 239/566x FOREIGN PATENTS 1,461,005 12/1966 France 134/172 PrimaryExaminerStanley H. Tollberg Assistant Examiner-Hadd S. LaneAttorney-Christen and Sabol ABSTRACT: Apparatus for cleaning filterelements comprising a plurality of nozzles for spraying water mountedasymmetrically with respect to the filter element to provide anasymmetric spray pattern whereby optimum utilization of the availablewater supply is obtained.

PATENTEU F'EB 1 s m SHEET 1 OF 4 3 [IJHHMM Roblkwmu Inventor M y O'M vM.

PATENTED FEB! 6 l97l SHEET 2 OF 4 I William ROBINSOA) Inventor by: 1%; vM

PATENIED FEB 16 ISTI 35631474 sum u 0F 4 a. mum Raw:

Inventor M M by: 0% Y W AIR FILTER WASH mzvrcs This invention relates tothe washing apparatus used to clean mechanical gas filter systems andrelates more particularly to an improved washer spray header forcleaning the filter panels of such mechanical filter systems.

In a mechanical gaseous filter for removing particulate matter from agas, the filter media or the collecting plates become loaded with dust.This leads to a reduction in the arrestive efficiency or an undesirableincrease in the pressure drop across the filter or both.

Some mechanical gas filter systems require removal of the filter panelswhich may then be thrown away or may be washed and returned to thesystem. Other systems are arranged for manual washing in situ.

In the interest of reducing the manual labor required to maintain theefficiency of the filter bank, systems using disposable filter mediahavebeen developed which embody filter media in the form of a roll whichcan be advanced periodically to present fresh filter media to theairstream. These rolls can be of substantial length, allowing manychanges of filter media in the air stream before the entire roll has tobe removed and replaced manually. This method reduces the manual laborrequired but is costly because the filter media is not recoverable.

In other mechanical air filters employing permanent filter media, thefilter panels have been arranged to pass down through the airstream intoan oil sump where the collected dust sludge is removed and the filterreoiled before passing back up again into the airstream. In still othersystems using permanent filter media, washing systems have been mountedon the filter bank to reduce the manual labor for washing. In theseconventional washing systems, evenly disposed spray nozzles are usedwhich are either fixed or mounted on a piece of pipe called a "standpipewhich may be disposed in a vertical plane reciprocally driven across thedownstream side of the filter. These supposedly automatic in situwashing devices are not fully automatic as they require frequent manualatten tion to attend to the relatively ineffective degree of cleaningwhich is achieved and to attend tothe relatively complex mechanicalcomponents. V

l years ago the most popular system were of the types embodyingpermanent media; however, due to the ineffectiveness and inefficiency ofthese types, the disposable roll type is now more often used. I proposea more effective and workable automatic cleaning system. This method issufficiently efficient and reliable to allow the use of permanent filtermedia. Although the method used in this application is automatic, I donot propose to clean while air is passing through the filter, and it isnecessary to either bypass the filter system, or arrange for cleaning ofa portion of the filter bank while routing the dust-laden gas throughanother portion of the bank, or shut down the fans.

According to my present invention, filters are automatically cleaned insitu with a system of fixed nozzles attached to a moving standpipe forspraying water on the filters. v

The nozzle arrangements that have been used up to the present time forwashing filters in situ are imperfect because the available water supplyis distributed in a regular pattern, which is generally insufficient onsome parts of the filter and wasteful on others.

It is therefore an object of this invention to clean filters with aspray pattern of delivery which optimizes the water supply available byforming an asymmetrical spray pattern which matches the washingrequirements of various parts of the filter and washes the various partsof the filter substantially evenly.

The proposed invention will function on normal water pressures, and, infact, improves the efficiency of washing with normal pressures. It isreadily seen that very high water pressures would have greater washingpower, but in most plant installations, only normal water pressure isfound and the best use must be made of it. Also, I have found thatwithout adding detergent or hot water, effective cleaning can beattained on filters of synthetic material by the asymmetrical spraypattern.

The present invention would undoubtedly be made even more efficient withhot water or detergent.

Another limitation of conventional devices for cleaning filters in situhas been the relative complexity of the mechanism employed to move thestandpipe header back and forth across the filters. The ei'tisting'systems use chain, cable, or worm and screw, arranged to support thestandpipe at both top and bottom in driving relationship with a track. Ipropose a system with standpipe or standpipes to be driven from the toponly.- This results in a substantial reductionin the amount of hardwareand associated equipment required. In addition, the existing systemsoften have the drive mechanism in the airstream, which permits dust andcleaning water to enter the moving parts and clog them. It isaccordingly a further aspect of my present invention to locate the drivemechanism for the standpipe out of the airstream to protect it from suchclogging. One or more standpipes may be provided and may be drivenreciprocally in a horizontal direction. More than one standpipe permits,among other things, a shorter distance of travel attention weekly.

It is yet another object of my present invention to provide a suitableasymmetrical nozzle arrangement.

The foregoing and other objects and advantages of my present inventionwill in part be stated in and in part become apparent from the followingdetailed description, when read in conjunction with the accompanyingdrawings, in which:

FIG. I is a perspective view of a filter disposed at an angle of 45 to avertical with a spray impinging thereon;

FIG. 2a is a cross-sectional view of a typical filter showing filterlayers therein;

FIG. 2b is an enlarged sectional view of a typical filter showing thewaterfiow pattern typically obtained with conventional spray-typeheaders;

FIG. 3 is a schematic view of a slot-type nozzle mounted at an angle tothe surface of the filter to produce an asymmetrical washing pattern ona typical filter;

FIG. 3a is a schematic plan view of the water pattern produced by thenozzle in FIG. 3, along the line 3a-3a of FIG.

FIG. 4 is a graph showing the relationship of the energy of impact e andthe concentration I: plotted against L, the overall length of the filtermeasured alongthe face of the filter from the top, for the nozzle shownin FIG. 3;

FIG. 5'is a schematic view depicting a nozzle with an irregularly shapedorifice vertically disposed to the face of the filter;

FIG. 5a is a schematic. plan view of the water pattern produced by thenozzle in FIG. 5 along the line 5a-5a of FIG.

FIG. 6 is a graph showing the function e( L) represented by a solid lineand the function c(L) represented by a phantom line, both plottedagainst L;

FIG. 7 is a composite graph showing for the three nozzle patterns shownin FIG. 7 the energy of impact and concentration functions, against thedistance of L from the top of the filter for an asymmetrical arrangementof nozzles;

FIG. 8 is a composite graph showing atypical nozzle pattern describedwith reference to its respective concentration energy and distancefunctions using a single symmetrical nozzle;

FIG. 9 is a composite graph showing typical nozzle patterns describedwith reference to their respective concentration, energy and distancefunctions using a symmetrical arrangement of three nozzles; and

FIG. 10 is a cutaway perspective view of an irregularly shaped nozzle.

Referring to the drawings, the device illustrated in FIG. 1 comprises anangularly inclined header 20, having nozzles 21, 22 and 23 located inspaced relationship thereon. Nozzle 21 is mounted closer to filter 15than nozzles 22 and 23 and delivers water at greater impact on filter 15than nozzles 22 and 23 by reason of its location on said header. Thefilter 15, collects dust from an airstream which impinges on its lowerside c so that the dust particles in theory are retained by filter l5and the cleaned air passes through on the upstream side adjacent to theheader. The media 14 for filter 15 may be made from any of a number ofknown commercial materials, and does not comprise a feature of thisinvennon.

Wash water emitted by the nozzles 21, 22 and 23 impinges on filter media14 in a predetermined pattern so that the latter receives complete watercoverage. Nozzle 21 covers a smaller area than nozzles 22 and 23 andprovides a flushing effect along the upper portion of the filter, anddust particles and wash water are then carried downwards along thefilter and through the lower side. Nozzle 21 is so designed that thewater emitted thoroughly washes the filter.

FIG. 1 also shows the relationship of L1, L2, and L3 to L as discussedin the mathematical description herein.

Referring to FIG. 2a, layer x( on the header or downstream side) ofinclined filter 15 consists of a layer of filtering medium. Layer y alsocomprises a filtering medium and layer 2 on the upstream side consistsof a form of screen.

FIG. 2b shows an unwetted area 17 occurring at the upper end of thefilter on the opposite side from the spray. This unwetted area 17remains unwashed by conventional spray-type headers.

Since filter banks tend to be quite large, often 100 or more squarefeet, there is a practical limitation on the quantity of water that canbe delivered to the installation per second. There are also practicallimitations to the amount of mainline pressure that can be madeavailable and maintained during the washing cycle. Therefore, the designof an effective washing spray pattern'can be viewed in terms ofmaximizing the usefulness of the pressure and volume available to theinstallation as well as in terms of the cost of volume and pressurerequired. To a large extent it has been the ineffective use of thevolume and pressure provided or available which has resulted in lessthan satisfactory performance of the many filter washing systemsdescribed in the prior art.

The effectiveness of the washing action depends on the volume of watersupplied per second, the velocity of the water and the total amount ofwater used.

A volume of water per second per unit area of the filter or lowconcentration 0 will tend to allow the water to trickle through thepaths of least resistance, leaving unwetted pockets, whereas a highconcentration c will tend to flood through even hydrophobic areas andfioat the dirt away.

The energy of impact e onany given area which is a function of thevolume of water per second falling on that area and the velocitysquared, will determine how far into the medium the water will penetrateunassisted by gravity and will also affect the scrubbing and floodingaction.

The total volume q that is required across each surface will be afunction of c and e and all the characteristics of the surfaces to becleaned.

If the filter was mounted horizontally, the analysis to find therequired volume would be quite simple. Values could be assigned to c, eand q making it possible through experimentation to develop a series ofvalues for the three variables and to determine the optimum combinationwith the lowest total volume of water through the filter to giveeffective washing. However, since the filters to be washed are generallymounted at an angle other than the horizontal and since the filter has afinite depth, the values ofc and e are different in various parts of thefilter and analysis becomes more complex. For example, referring to FIG.2b it can be noted that:

l. The energy of impact e diminishes rapidly as the water penetrates thefilter.

2. Concentration c in the lower parts of the filter 15 are reinforced bywater running down from above.

3. While gravity will carry water through the filter in lower portions,impact energy alone must carry it through to the topmost rear part ofthe filter, (17).

4. The impact absorbing and permeable characteristics of the variouslayers of material in the filter will effect c and e in different ways.

It follows that the minimum values of c, and e required for effectivewashing will be higher in the top part of the filter than those requiredin the lower parts. This suggests an experimental procedure fordetermining these values in which the behavior of the water is examinedin segments down the filter from the top.

EXPERIMENTAL PROCEDURE To determine the most effective arrangement ofnozzle or nozzles in a header delivering a pattern of water along avertical plane to the filter face:

1. Fix the pressure p, at the nozzles, this pressure being the same forall the nozzles.

2. For different s, (describing the size and shape of the top nozzle)find in each case the longest possible L (the vertical dimension of'thearea of wash) leading to satisfactory cleaning of the top part of thefilter. These results can be expressedby the formula L, f, (s,).

. For fixed s, using the corresponding L, f,(s,) and a different s findthe longest possible L leading to satisfactory cleaning of the secondportion of filter. This leads -to the formula L f s,(s). Severalsuchformulas, depending on different s, can be expressed by theformula 1. =f (s,sr.).

4. Similarily for fixed s, and s with corresponding L, =f,(s,

) and L =f (s, obtain formula L, =fs, (s leading to L =f (s, s It is acondition of the system that L,

L L}, L (see FIG. 1). The number of nozzles n required will depend onthe sizes s,s s,-,.

TECHNIQUE The total cost or efficiency of washing the filter will be thesum of the cost of water/ 1,000 cubic feet 0 plus the cost ofmaintaining the mainline supply pressure P; the latter will be thepressure required at the nozzles, p, plus the pressure drop from themainline to the nozzles for the volume/second required. Having developeda cost formula in terms of s and p which will have the form fault p 1 23) it is possible to optimize the cost of various values of n,, n n,-where n equals the number of nozzles necessary to cover L.

The experimental procedure can be repeated for a different pressure pand the costs optimized with fire p 1 2 a) The optimum s and p can befinally refined by f (n, s) where where n represents the initial cost ofn nozzles and s represents the operating maintenance cost as a functionof nozzle size; the smaller the nozzlegthe higher the risk of plugging,and hence the higher the maintenance cost.

The above procedure establishes the optimum asymmetrical pattern in avertical plane through the filter under static conditions, i.e. nohorizontal movement of the nonle assembly. It is now necessary tocalculate the maximum rate of horizontal travel h possible.

The value of h flows from an examination of each vertical segment of thefilter under the conditions of the optimum pattern for the value of qand the width of the spray pattern at that segment. The maximum rate ofhorizontal travel will be the rate which will deliver the minimum qrequired per unit area. It is obvious that if the rate of horizontaltravel is too great, the filter media will not be sufficiently flushedthroughout its thickness--q per unit area will be too low. If the rateof travel is too slow, q will be greater than necessary, and water andtime to clean the filter will be wasted.

It can be deduced, and experimentation verifies, that a plot of theminimum values for c and e required to give effective cleaning can bedescribed by the formulas:

where L is the distance measured down the face from the top of thefilter (see FIGS. 1 and 6). k will depend on the minimum energy ofimpact e required to effectively wash the first layer .1: (see FIG. 2b)and to impart sufficient turbulent energy to the water in the center ofthe filter y. For best results k will be more than twice k and allvalues of k must be positive. k k will be the energy e required to forcewater through the filter unassisted by gravity at the top where L O asin (l above.

a and B depend on the shape of the spray pattern and depend on thenature of the filter, and have arbitrarily assigned values. Generally aand B are each greater than 6 for thick filters and less than 6 forthinner filters, but they are not critical values.

k will be a function of gravity, the angle of the filter to thehorizontal and the energy absorbing characteristics of the variouslayers of materials in the filter.

k will depend on the minimum concentration c of water to flood all partsof the first layer x and to supplement the water running downwardsinside the filter and escaping through layer z.

k will be the amount of water required in the top portions to prime therundown phenomenon in the filter.

k will be a function of gravity, the angle of the filter to thehorizontal and the permeability characteristics of the various layers ofmaterial in the filter.

It will be noted in selecting various nozzles for evaluation that forany given pressure and quantity of water the greatest energy of impact eand concentration c for any given zone extending from the upper to thelower end of the filter will be achieved with nozzles producing a fiat,slot-like spray pattern. Such a slot-like pattern can be given 10 totimes the values that the same volume and pressure would be given with around or square pattern.

With these facts in mind, and in particular knowing the general form ofthe optimum curves for e and c, as described above and shown in FIG. 6,it is possible to approximate the values of k,, k k k.,, k and k,; for aparticular filter mounted at a certain angle to the horizontal whichwill greatly reduce the number of experiments in the experimentalprocedure required to obtain the pertinent data for the efficiencyoptimizing calculations.

FIG. 1 shows an arrangement embodying three nozzles designed to give anasymmetrical delivery. In the event the nozzle number 21 delivers 3g.p.m. at 40 psi. from a distance of 2 inches, nozzle number 22 delivers2 g.p.m. at 40 p.s.i. from a distance of 3.5 inches and nozzle number 23delivers l g.p.m. at 40 p.s.i. from a distance of 3.5 inches. Thebenefits that accrue from this asymmetrical delivery pattern can be seenin FIG. 7 where curve number 1 represents the minimum down water addedfor the asymmetrical nozzles. The resultant c and e from theasymmetrical heads of FIG. I are plotted as curves 4 and 5 respectively.

A single nozzle mounted vertically over the center of the filterdelivering the same volume, i.e. 6 g.p.m. at 40 p.s.i. would give theresults shown by curves 7, 8 and 9 in FIG. 8, which is not quiteadequate in the bottom percent of the filter and totally ineffective inthe top 30 percent. Theoretically, a single nozzle would have to deliver60 to 120 g.p.m., 10 to 20 times that of the asymmetrical arrangement toeffectively clean the same filter.

The results obtained from three nozzles of 2 g.p.m. each at 40 p.s.i.mounted without asymmetry are shown by curves 10, 11 and 12 in FIG. 9.While this is better than the results from a single nozzle, it will benoted that it falls percent short of providing effective cleaning in thetop 20 percent of the filter and cleaning water is wasted in the bottompercent. Three nozzles without asymmetry would have to deliver a totalof 20 to 30 g.p.m. to effectively clean all the filter.

FIGS. 3, 4 and 5 illustrate other methods of obtaining an asymmetricaldelivery of water to the filter face.

I claim:

I. In filter cleaning mechanisms for a rectangular gas filter ing mediumhaving a flat surface in a plane inclined with respect to thehorizontal, the combination including header assembly means to bereciprocally moved in a horizontal direction parallel with the surfaceof the filtering medium, and means for connecting said header assemblymeans with a source of cleaning fluid during said reciprocal movement,said header assembly means also including nozzle means for directing aband of said cleaning fluid to the upper surface of the filtering mediumextending across the entire surface between the upper and lower marginsthereof and generally transverse to the direction of said reciprocalmovement of the header assembly means, said band being narrow withrespect to the height of said filtering medium, said nozzle means alsoincluding means for directing a greater concentration of fluid in saidnarrow band to areas of the filtering medium adjacent the upper marginof the filtering medium than to areas of the filtering medium lyingtherebelow.

2. The invention defined in claim 1, wherein said nozzle means includesan outlet orifice having an irregular cross section, whereby a greateramount of fluid is directed toward the end of said narrow band adjacentthe upper margin of the filtering medium.

3. The invention defined in claim 1, wherein said nozzle means includesat least two outlet orifices disposed in alignment transverse withrespect to the direction of said reciprocal movement, the orificedisposed adjacent to the upper margin of the filtering medium beingdisposed closer to the surface thereof than another orifice.

4. The invention defined in claim 1, wherein said nozzle means includesa generally vertical header assembly provided with more than one nozzlefor communicating with cleaning fluid supply.

5. In a system for cleaning filter elements having a header assembly,support structure for said header assembly and drive means for producingreciprocal movement of said header assembly across the surface of afilter element as defined in claim 4, the improvement comprising aseries of more than one nozzle mounted on said vertical header assemblyand communicating with a water supply, said series having at least onenozzle disposed in a spaced relationship with the filter so that theenergy of impact and the concentration of water at the surface of thefilter are described according to the following relationship:

where e( L) is energy of impact; k k is energy 2(0) and are as follows:the energy (1 is a constant;

c( L) is the concentration at a given point;

k k is the concentration 0(0);

k will depend on the minimum concentration c of water to flood all partsof the first layer x and to supplement the water running down inside thefilter for which is lost at the back (layer z);

will be the amount of water required in the top portions to prime therundown phenomenon in the filter;

is a function of gravity, the angle of the filter to the horizon and thepermeability characteristics of the various layers of material in thefilter; and B is a constant. 6. In a system for cleaning filter elementshaving a header assembly, support structure for said header assembly andmeans for producing reciprocal movement across the surface of a filterelement, drive said means adaptable to advance and to retard said headerassembly in said support structure as defined in claim 4, theimprovement comprising more than one nozzle whose apertures produce aspray pattern whose general characteristics of energy of impact andconcentration are described in accordance with the formulas set outbelow:

k k is energy e (0); L is the distance measured down the face from thetop of the filter;

is a constant;

is the concentration at a given point; will depend on the minimumconcentration 0 of water to flood all parts of the first layer at and tosupplement the water running down inside the filter for which is lost atthe back (layer z);

will be the amount of water required in the top portions to prime therundown phenomenon in the filter;

is a function of gravity, the angle of the filter to the horizon and thepermeability characteristics of the various layers of material in thefilter; and

is a constant.

a C(L) 4 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3563, 47 Dated February 16, 1971 Inventofls) Joseph William RobinsonIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

column 3, line H8, insert -low-- before "volume"; column 3, line #9,cancel "low"; column 5, formula (1), that portion of the formula column5, formula (2), that portion of the formula reading 5 L B should read Q5 Signed and sealed this 1st day of, May 1973.

reading 2 L C should read (SEAL) l Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PC4050 (IO-69) uscoMM-oc cos?

1. In filter cleaning mechanisms for a rectangular gas filtering mediumhaving a flat surface in a plane inclined with respect to thehorizontal, the combination including header assembly means to bereciprocally moved in a horizontal direction parallel with the surfaceof the filtering medium, and means for connecting said header assemblymeans with a source of cleaning fluid during said reciprocal movement,said header assembly means also including nozzle means for directing aband of said cleaning fluid to the upper surface of the filtering mediumextending across the entire surface between the upper and lower marginsthereof and generally transverse to the direction of said reciprocalmovement of the header assembly means, said band being narrow withrespect to the height of said filtering medium, said nozzle means alsoincluding means for directing a greater concentration of fluid in saidnarrow band to areas of the filtering medium adjacent the upper marginof the filtering medium than to areas of the filtering medium lyingtherebelow.
 2. The invention defined in claim 1, wherein said nozzlemeans includes an outlet orifice having an irregular cross section,whereby a greater amount of fluid is directed toward the end oF saidnarrow band adjacent the upper margin of the filtering medium.
 3. Theinvention defined in claim 1, wherein said nozzle means includes atleast two outlet orifices disposed in alignment transverse with respectto the direction of said reciprocal movement, the orifice disposedadjacent to the upper margin of the filtering medium being disposedcloser to the surface thereof than another orifice.
 4. The inventiondefined in claim 1, wherein said nozzle means includes a generallyvertical header assembly provided with more than one nozzle forcommunicating with cleaning fluid supply.
 5. In a system for cleaningfilter elements having a header assembly, support structure for saidheader assembly and drive means for producing reciprocal movement ofsaid header assembly across the surface of a filter element as definedin claim 4, the improvement comprising a series of more than one nozzlemounted on said vertical header assembly and communicating with a watersupply, said series having at least one nozzle disposed in a spacedrelationship with the filter so that the energy of impact and theconcentration of water at the surface of the filter are describedaccording to the following relationship:
 6. In a system for cleaningfilter elements having a header assembly, support structure for saidheader assembly and means for producing reciprocal movement across thesurface of a filter element, drive said means adaptable to advance andto retard said header assembly in said support structure as defined inclaim 4, the improvement comprising more than one nozzle whose aperturesproduce a spray pattern whose general characteristics of energy ofimpact and concentration are described in accordance with the formulasset out below: